1. Field of the Invention
The present invention relates generally to an apparatus and method of controlling emitting colors of a visible light emitting diode (LED). More particularly, the present invention relates to controlling the emitted colors according to a current communication state in a visible light communication (VLC) device.
2. Description of the Related Art
Due to the improved technological performance and reduced cost of light emitting diodes (LEDs) in recent years, such LEDs have rapidly proliferated in the fields of specialized lighting, such as lights used in portable devices, displays, automobiles, traffic lights, sign boards, etc., and so on. In particular, LEDs are also becoming increasingly popular for use as camera flashes, as well as portable flashes for mobile phones or personal digital assistants (PDAs), backlight units for LCDs, and other applications. More recently, due to radio frequency (RF) band depletion, and the collision probability of different wireless communication technologies, as well as the emergence of ultra high-speed ubiquitous communication environments in a 4 G wireless technology, concerns about the optical wireless communication technology being used in a complementary system along with RF communication technology has increased. Thus, the research and development of optical wireless communication technology using LEDs is being extensively conducted by a number of companies and research institutions.
There have been a number of studies of peripheral interfaces enabling communication from one device to another using an infrared data association (IrDA) module mounted on portable devices such as a mobile phone or PDA, a small-sized home appliance such as a digital camera or MP3 player, and so on. Due to such studies, a variety of products associated with such peripheral interfaces have been developed and commercialized. The optical wireless communication technology including infrared communication offers several advantages such as non-congestion between different devices, ensured communication security, low implementation cost, and so on, which is an improvement over radio frequency (RF) communications such as Bluetooth or ZigBee. In order to implement optical communication, LEDs can be advantageously used instead of IrDa modules because of technological merits and better cost effectiveness, when compared with IrDA modules.
One of the advantages of visible light communication using a visible LED as a peripheral interface is that an LED module which is pre-mounted on a mobile terminal or PDA can be utilized without the need to install additional modules. In addition, the use of the LED module facilitates pointing between transceiver modules or devices., Additionally, a more aesthetic appearance is presented by the LED module, and when compared to IR communication, has been shown to have better results capturing a consumer's attention.
Visible light communication in general normally employs data communication schemes using blinking light signals and/or different colors light signals to facilitate the communication. That is to say, communication between visible light communication devices is performed via at least one of blinking or color control of light signals.
With reference to FIG. 1, a visible light communication (VLC) device 100 transmits desired data to a counterpart VLC device 102 through a visible light signal (referred to as 110 in FIG. 1) by driving a visible LED. The VLC device 102, which employs a camera to serve as a receiver for receiving a visible light signal, analyzes visible light signals received through the camera and communicates with the VLC device 100.
One of the drawbacks of communication between VLC devices is that a user has difficulty in directly checking the current communication state of the device, for example, to monitor items such as establishment of a communication link, progress of data communication, or receive feedback about the stability of the communication link established depending on position or angle between mobile terminals.
In addition, with regard to conventional VLC technology, light of the same color as that emitted during data transmission is emitted from an LED of the VLC device, even during an initialization procedure such as detection of VLC devices, negotiation after the detection, and the like. Furthermore, even when a communication link established between the two VLC devices is disconnected in the course of data transmission, a user cannot identify the disconnection.